The present invention concerns improved hard-soft ionomeric resin mixtures (or blends) which are particularly well suited for the formulation of the cover composition of a golf ball. In addition, the present invention is directed to the improved low modulus golf balls produced utilizing the cover compositions of the invention.
More specifically, the present invention relates to novel golf ball cover compositions of low modulus blends comprising about 25 to about 10 (preferably from less than 25 to about 15) weight percent of hard ionomer resins and from about 75 to about 90 (preferably from greater than 75 to about 85) weight percent of soft ionomer resins. The new compositions of the present invention, when utilized for golf ball construction, particularly the construction of two piece golf balls, produce golf balls exhibiting enhanced playability (spin rate) characteristics without substantially sacrificing such properties as travel distance, roundness, impact resistance and/or durability.
Ionomeric resins are polymers containing interchain ionic bonding. As a result of their toughness, durability, and flight characteristics, various ionomeric resins sold by E.I. DuPont deNemours & Company (see U.S. Pat. No. 4,884,814) under the trademark "Surlyn.RTM. and more recently, by the Exxon Corporation (see U.S. Pat. No. 4,911,451) under the trademarks "Escor.RTM." and the tradename "Iotek", have become the materials of choice for the construction of golf ball covers over the traditional "balata" (trans polyisoprene, natural or synthetic) rubbers. The softer balata covers, although exhibiting enhanced playability properties, lack the durability necessary for repetitive play.
Ionomeric resins are generally ionic copolymers of an olefin such as ethylene and a metal salt of an unsaturated carboxylic acid, such as acrylic acid, methacrylic acid, or maleic acid. Metal ions, such as sodium or zinc, are used to neutralize some portion of the acidic groups in the copolymer resulting in a thermoplastic elastomer exhibiting enhanced properties, i.e. improved durability, etc., for golf ball cover construction over balata. However, the advantages gained in increased durability have been offset to some degree by the decreases produced in playability. This is because although the ionomeric resins are very durable, they tend to be very hard when utilized for golf ball cover construction, and thus lack the degree of softness required to impart the spin necessary to control the ball in flight.
As a result, while there are currently more than fifty commercial grades of ionomers available from DuPont and Exxon with a wide range of properties which vary according to the type and amount of metal cations, molecular weight, composition of the base resin (i.e. relative content of ethylene and methacrylic and/or acrylic acid groups) and additive ingredients such as reinforcements, etc., a great deal of research continues in order to develop golf ball cover compositions exhibiting not only the improved impact resistance and carrying distance properties produced by the "hard" ionomeric resins, but also the playability (i.e. "spin") characteristics previously associated with the "soft" balata covers, properties which are still desired by the more skilled golfer.
In various attempts to produce such an ideal golf ball, the golfing industry has blended the hard ionomeric resins with a number of softer polymeric materials, such as softer polyurethanes. However, the blends of the hard ionomer resins with the softer polymeric materials have generally been dissatisfactory in that these balls exhibit numerous processing problems. In addition, the balls produced by such a combination are usually short on distance.
In addition, various "hard-soft ionomeric blends", i.e. mixtures of ionomer resins which are significantly different in hardness and/or flexural modulus, have been attempted. However, until the development of the specific blend combination set forth in U.S. Pat. No. 4,884,814, directed to relatively low modulus golf ball cover compositions, these balls were not particularly commercially viable. In this regard, although the balls produced using the hard-soft ionomer blends exhibited enhanced playability characteristics, they lacked the durability needed for continuous play.
U.S. Pat. No. 4,884,814, one of the inventor's previous patents, is directed to the finding that if various "hard" methacrylic acid based ionomer resins (i.e. those ionomer resins having a hardness of about 60 to 66 on the Shore D scale as measured in accordance with ASTM method D-2240) were blended with similar or larger quantities of one or more "soft" ionomer methacrylic acid based ionomer resins (i.e. those ionomer resins having a hardness from about 25 to 40 as measured on the Shore D scale) that relatively low modulus golf ball cover compositions could be produced that are not only softer than the prior art hard ionomer covers but also exhibit a sufficient degree of durability for repetitive play. These relatively low modulus cover compositions were generally comprised of from about 25 to about 70 weight percent of hard ionomer resins and from about 30 to about 75 weight percent of soft ionomer resins. The incorporation of larger percentages of soft ionomer resin into the cover formulations was generally deemed to be undesirable due to the sacrifices in distance and/or durability that were produced thereby.
However, notwithstanding the above, it has now been found that specific hard/soft ionomer resin blends comprising from about 25 to about 10 (preferably from less than 25 to about 15) weight percent of one or more hard ionomer resins and from about 75 to about 90 (preferably from greater than 75 to about 85) weight percent of one or more soft ionomer resins offer, when utilized for golf ball cover construction, particular advantages to the high skilled professional golfer. Specifically, it has been found that golf balls produced using the new low modulus cover compositions of the invention exhibit high spin rates at very low club head speeds. These balls offer particular utility for the highly skilled and/or professional golfer who desires greater control on the low club head speed "pitch" or "wedge" shots.
In the past, covers composed of high levels of soft ionomers were considered to be nonfunctional due to the drop off in C.O.R. (i.e. travel distance) and cut resistance that accompanied the increase in softness. However, for the P.G.A. Touring Professional Golfer and other highly skilled golfers, distance and durability are generally not a concern. Along these lines, the P.G.A. Touring Professional Golfer will almost never mis-hit a ball badly enough to cut the cover. In addition, the club head speed generated by professional golfers is typically much higher than the amateur, thereby producing greater distance. Thus, the resilience characteristic of the ball is of less importance for the professional golfer than for the average player.
Moreover, the P.G.A. Touring Professional Golfer is usually willing to sacrifice distance for added control, particularly with respect to shots around the green. It is in these pitch, or half and quarter wedge shots that the balls of the present invention show a distinct advantage over the hard/soft ionomer blends of the prior art and the balata covered wound balls.
The present invention is directed to new golf ball cover compositions which exhibit properties of enhanced playability characteristics (i.e. softness and spin) over known hard-soft ionomer blends and the balata-covered wound balls. It has been found that these properties can be produced using improved hard-soft ionomer blends of the present invention in order to produce a low modulus golf ball cover.
The foregoing has outlined some of the most pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention, the detailed description of the invention and the claims which follow below.